Etching method of organic insulating film

ABSTRACT

This invention relates to a method for etching an organic insulating film used in the production of semiconductor devices. A sample to be etched on which a low dielectric constant organic insulating film is formed and is etched by generating a plasma from hydrogen gas and nitrogen gas or ammonia gas, and controlling the gas flow rate and pressure so that the light emission spectral intensity ratio of hydrogen atom and cyan molecule in the plasma comes to a prescribed value. By this method, a low dielectric constant organic insulating film as an insulating film between layers can be etched without using any etch stop layer so that bottom surface of trenches and holes for electrical wiring become flat.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an etching method of organic insulating films,and particularly to an etching method suitable for etching organicinsulating films used in the production of semiconductor devices.

2. Description of the Related Art

[Prior Art 1]

As a method for etching an organic insulating film while preventing themicrotrenching without using etch stop layer, for example, the method ofWO 01/15213 A1 (JP-A-2001-60582) is known. The gazette of theabove-mentioned patent gives the following description.

Thus, the wafer temperature is maintained at 20-60° C., in accordancewith the processing. Then, a gaseous mixture of N₂, H₂ and Ar isintroduced into the processing chamber. The inner pressure of theprocessing chamber is adjusted to 500 mTorr or more substantially, andpreferably 500-800 mTorr substantially. Then, a radio-frequency voltagehaving a frequency of 13.56 MHz and a power of 600-1,400 W is applied tothe lower electrode, and a radio-frequency power having a frequency of60 MHz and a power of 600-1,400 W is applied to the upper electrode. Bytaking such a measure, a high-density plasma is generated in theprocessing chamber and, due to the plasma, contact holes of a desiredshape are formed in the insulating layer between layers of wafer made ofan organic low-dielectric constant material.

Further, the same gazette as above makes the following mention, too.

A treating gas containing at least a nitrogen atom-containing gas and ahydrogen atom-containing gas is introduced into the processing chamber,and the inner pressure of the vacuum processing chamber is adjustedsubstantially to 500 mTorr or more to carry out etching of the organiclayer film formed on the wafer to be etched placed in the processingchamber. As the material constituting the organic film, a low-dielectricconstant material having a relative permittivity of 3.5 or less ispreferable. The inner pressure of the vacuum processing chamber ispreferably kept at 500-800 mTorr substantially.

By using a gas containing at least a nitrogen atom-containing gas and ahydrogen atom-containing gas as the processing gas and adjusting theinner pressure of the vacuum processing chamber substantially to 500mTorr or higher, microtrenching can be prevented without using etch stoplayer and the mask-selection ratio can be enhanced. Such a technique isespecially effective for processes which require to stop the etching inthe midst of an organic layer film, such as the dual damascene process,or the like.

It is possible to use N₂ as the nitrogen atom-containing gas or to useH₂ as the hydrogen atom-containing gas, if desired. In the gazettereferred to above, there are mentioned some examples in which the N₂/H₂flow rate ratio (N₂/H₂) is 400 sccm/400 sccm, 200 sccm/200 sccm, and 100sccm/300 sccm.

[Prior Art 2]

As another method for etching an organic insulating film, the method ofJP-A-2000-252359 is known. The following description is given in thegazette thereof.

An insulating film (insulating film) between layers made of an organicdielectric film such as polyallyl ether is subjected to etching, whileforming a CN group-containing reaction product, etc. by the use of an NHgroup-containing ion or radical generated from a gas plasma made from amixture of hydrogen and nitrogen or an ammonia-containing gas.

The etching process of the insulating film between layers is carried outby means of ECR type (Electron Cyclotron Resonance type) plasma etchingapparatus under conditions of, for example, a substrate-providedelectrode temperature of 20° C., a μ-wave power (2.45 GHz) of 2,000W, apressure of 0.8 Pa, an RF power of 300 W, by using NH₃ as an etching gasat a flow rate of 100 sccm.

In the etching process mentioned above, it is also possible, if desired,to carry out the etching process by the use of a gas plasma comprising agaseous mixture of hydrogen and nitrogen at a flow rate (N₂+H₂) of, forexample, 100 sccm at a H₂/N₂ flow rate ratio of, for example, 75/25sccm.

By carrying out the etching using NH group-containing ion or radical, aninsulating film containing an organic dielectric film can be subjectedto an anisotropic etching without forming a damage layer causingdefective conduction, while suppressing side etching, while maintaininga high etch rate of about 450 nm/minute, without bringing about areduction of throughput, and rapidly.

By such a technique, it is also possible to etch an insulating filmcontaining an organic insulating film to open contact holes. Thistechnique is applicable also to an etching process for forming trenchfor interconnect wiring such as damascene process, or to an etchingprocess for simultaneously opening trench for interconnect wiring andcontact hole such as dual damascene process, etc.

Further, if etching process of insulating film between layers is carriedout under various conditions [(a) N₂=100 sccm, (b) N₂/H₂=50/50 sccm and(c) H₂=100 sccm] and emission spectra are measured, an NH peakobservable neither in the case (a) using N₂ gas nor in the case (c)using H₂ gas is observed in the case (b) using N₂/H₂ mixture. Further,as for CN peak, the peak intensity observed in the case (b) using N₂/H₂mixture is higher than the peak intensity in the case (a) using N₂ gasand in the case (c) using H₂ gas.

Further, if the flow rate ratio of etching gas is so varied thatN₂/H₂=100/0 to 50/50 to 0/100 sccm and the relative etch rate (the etchrate at N₂/H₂=100/0 sccm is taken as 1) and the emission spectralintensity ratios between the light-emitting components (CN, NH, N₂, CH,H) at varied flow rate ratios are measured, it is found that the etchrate and the emission spectral intensity ratio between CN and NH areroughly the same in the behavior.

SUMMARY OF THE INVENTION

In the recent years, a damascene process using copper has been used as amethod for forming a wiring on semiconductor elements. As an applicationof the damascene process, a dual damascene process can be referred to.In the prior dual damascene, an etch stop layer has been used forpreventing the sub-trenching which is sometimes called “microtrenching”,at the time of forming a trench for interconnect wiring leading to theorganic insulating film functioning as an insulating film betweenlayers. Since an etch stop layer has a high dielectric constant,however, it is attempted today to lower the dielectric constant withoutusing any etch stop layer.

According to the former prior art mentioned above (JP-A-2001-60582),etching of organic layer film is performed while keeping the innerpressure of vacuum processing chamber at 500 mTorr (ca. 66.5 Pa) orabove, and preferably at 500-800 mTorr. According to this etchingmethod, however, inner pressure of the processing chamber is very high,and hence this method is expected to have the following problems: (1) inthe case of samples having a large diameter such as 300 millimeterwafer, the waste gas generated as a reaction product from the wafersurface cannot sufficiently be removed at the central part of wafer, sothat the etch rate within the wafer surface is not uniform, (2) thequantity of reaction product is so large that controlling the shape oftrench and hole is difficult, and (3) the quantity of reaction productis so large that inside of processing chamber is apt to be soiled, whichreduces reproducibility of the etching treatment. Accordingly, a measurefor solving these problems have to be taken when the processing is to becarried out at a high processing pressure.

On the other hand, the latter prior method (JP-A-2000-252359) is knownas a method for etching an organic insulating film at a low processingpressure (0.8 Pa) which makes it unnecessary to consider theabove-mentioned problems in the etching process at a high processingpressure. The latter prior method, however, pays no consideration forthe problem occurring when an organic insulating film of dual damasceneprocess is etched while preventing microtrenching without using etchstop layer.

According to the latter prior art, an organic insulating film is etchedwith an NH group-containing ion or radical generated by gas discharge orthe like in a hydrogen-nitrogen gas mixture or ammonia gas mixture as aprocessing gas, while forming a CN group-containing reaction product,etc. However, this technique is unable to prevent the microtrenchingwithout using etch stop layer at any flow rate ratio ofhydrogen-nitrogen mixed gas or ammonia-containing gas.

The etching method of the latter prior art is a method in whichattention is paid to the fact that etch rate and CN/NH emission spectralratio are roughly the same in behavior. Accordingly, this method has aproblem that the optimum condition of etching cannot be selected on thebasis of CN/NH emission spectral intensity ratio, and the optimumcondition for etching an organic insulating film while preventingmicro-trenching without using etch stop layer cannot be selected.

The phenomenon that a microtrenching (sometimes called “sub-trenching”,too) is formed and thereby the bottom surface of the trenches or holesof the etched part become impossible to flatten is attributable to thefollowing fact. The etch rate is higher in the neighborhood of sidewallof trenches and holes than in the central parts of the trenches andholes due to collision of the incident ion originated from the plasmaagainst the sidewall, caused by the slight taper of the sidewall oftrenches and holes which are the part to be etched, followed byconcentration of the incident ion into the neighborhood of sidewall oftrenches and holes, or due to a re-deposition of various reactionproducts formed by the etching to the central parts of trenches andholes.

It is an object of this invention to solve the problems mentioned aboveby providing an etching method of organic insulating film which makes itpossible to perform etching of an organic insulating film whilesuppressing the re-deposition of reaction products onto inner walls ofprocessing chamber and preventing the microtrenching.

The above-mentioned object can be achieved by an etching method oforganic insulating film which comprises generating a plasma from amolecular gas containing hydrogen atom and nitrogen atom, measuring theemission spectral intensity ratio between hydrogen atom and cyanmolecule in the plasma, and carrying out the processing while keepingthe measured value of the ratio at a prescribed value or under.

In this invention, there is used a plasma in which the emission spectralintensity ratio CN/H between the emission spectrum of hydrogen (H) at awavelength of about 486 nm and that of cyan molecule (CN) at awavelength of about 388 nm is 1 or less.

Further, the above-mentioned object can be achieved by generating aplasma from hydrogen gas and nitrogen gas or ammonia gas, and performingan etching method of organic insulating film while controlling the flowrate of hydrogen gas so that the emission spectral intensity ratiobetween hydrogen atom and cyan molecule in the plasma comes to aprescribed value or under.

The processing is carried out while controlling the processing pressureat a constant value.

Further, the above-mentioned object can be achieved by supplying anitrogen gas and a hydrogen gas or a molecular gas containing hydrogenatom and nitrogen atom into an etching process chamber in which isplaced a sample to be etched forming an organic insulating film,adjusting the inner pressure of the etching process chamber to apressure lower than 10 Pa, thereby generating a plasma in which theintensity ratio CN/H between an emission spectrum of hydrogen atom (H)at a wavelength of about 486 nm and an emission spectrum of cyanmolecule (CN) at a wavelength of 388 nm is 1 or less, and processing thesample to be etched with said plasma.

For generating of the plasma, a hydrogen gas and a nitrogen gas areused, and the mixing ratio of the hydrogen gas to the nitrogen gas isadjusted to 10 or more. Further, total flow rate of the hydrogen gas andnitrogen gas is adjusted to 200 cc/minute or more.

Alternatively, a hydrogen gas is used as the molecular gas containinghydrogen atom, an ammonia gas is used a the molecular gas containingnitrogen atom, and the mixing ratio of the hydrogen gas to the ammoniagas is adjusted to 10 or more. Further, the total flow rate of thehydrogen gas and the ammonia gas is adjusted to 200 cc/minute or more.

According to another embodiment of this invention, the above-mentionedobject can be achieved by generating a plasma in the process chamber,measuring the emission spectral intensity ratio between cyan moleculeand hydrogen atom in the plasma, controlling the flow rate-controllingvalves so as to keep the measured value at a prescribed value or under,and etching the sample to be etched, by the use of an apparatus equippedwith a sample stand on which a sample to be etched can be placed, anair-leakless process chamber into which an etching gas is fed, a vacuumpump evacuating the inner space of process chamber to a reducedpressure, flow rate-controlling valves which can control the flow ratesof hydrogen gas and nitrogen gas or a molecular gas containing hydrogenatom and nitrogen atom, a gas exhaust rate-controlling valve which isplaced between the vacuum pump and the process chamber to control theexhaust rate of the etching gas fed into the process chamber, a circuitand an electric source to which the electric power for generating aplasma from the etching gas in the process chamber can be applied, and avacuum gauge for measuring the pressure in the process chamber. The flowrate-controlling valves are controlled so as to increase the flow rateof hydrogen gas. Further, the gas exhaust rate-controlling valve iscontrolled so as to keep constant the inner pressure of the processchamber.

The sample to be etched is etched while controlling the output ofelectric source for generating a plasma from the etching gas so as tokeep the measured value at a prescribed value or under. The electricsource is controlled so as to increase the output and thereby toincrease generation of hydrogen atom in the plasma.

Further, an electric source capable of inputting a bias voltage to thesample to be etched is connected to the sample stand, and the electricsource is controlled so as to lower the bias voltage and thereby keepthe measured value at a prescribed value or under.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view illustrating one exampleof the etching apparatus for carrying out the etching method of thisinvention.

FIG. 2 is a plan view illustrating the whole of the plasma etchingapparatus provided with the etching apparatus of FIG. 1.

FIG. 3 is a flow chart illustrating an etching process using theapparatus of FIG. 2.

FIGS. 4A-4F are longitudinal cross sectional view illustrating the shapeof cross section of etching of a wafer according to the etching flowshown in FIG. 3.

FIG. 5 is a figure illustrating the light emission intensity of a plasmain the subtrench-free etching process in an interconnect wiring trenchprocessing of an organic insulating film.

FIG. 6 is a figure illustrating the light emission intensity of a plasmain a subtrench-forming etching process in an interconnect wiring trenchprocessing of an organic insulating film.

FIG. 7 is a cross sectional view illustrating the shape of cross sectionof etching which has been subjected to etching in the state of theplasma light emission intensity shown in FIG. 5.

FIG. 8 is a cross sectional view illustrating the shape of cross sectionof etching which has been subjected to etching in the state of theplasma light emission intensity shown in FIG. 6.

FIG. 9 is a figure illustrating the relation between the light emissionintensity ratio CN/H between cyan molecule and hydrogen atom in a plasmaand sub-trenching, in an interconnect wiring trench processing of anorganic insulating film.

FIG. 10 is a chart illustrating the flow for suppressing thesub-trenching in an interconnect wiring trench processing of an organicinsulating film.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereunder, one example of this invention is explained by referring toFIGS. 1 to 10.

FIGS. 1 and 2 illustrate one example of the plasma etching apparatus forcarrying out the etching method of this invention, wherein FIG. 1illustrates an outlined construction of the etching process chamber, andFIG. 2 illustrate the whole of the plasma etching apparatus providedwith the etching process chamber of FIG. 1.

In the vacuum chamber 11, a sample stage 24 is provided, on which wafer2, namely a sample to be etched, can be set. The sample stage 24 isconnected to a high-frequency electric source 25 (for example, frequency800 kHz) for bias voltage which gives a bias voltage to wafer 2. Sample24 is connected also to a temperature controlling apparatus 26 forcontrolling the temperature of wafer 2.

In the upper part of the vacuum container 11 is formed a cylindricalprocess chamber. Outside the process chamber of the vacuum chamber 11 isprovided magnetic field-generating coils 23 a and 23 b so as to envelopthe process chamber. In the upper part of the process chamber in thevacuum chamber 11 is provided a plate antenna 13 composed of anelectroconductive material so as to confront the sample stage 24 throughintermediation of a dielectric body 12 through which an electromagneticfield can propagate. In the upper part of the plate antenna 13 isprovided a coaxial line 15, via which the antenna is connected to ahigh-frequency electric source 16 (for example, frequency 450 MHz) forgenerating a plasma.

On the plate antenna 13 is formed a gas feeding line 14 having athrough-holes for supplying an etching gas into the process chamber. Thegas feeding line 14 is connected to gas tanks 20, 21 and 22 via flowrate controlling valves 17, 18 and 19, respectively.

In the bottom part of the vacuum chamber 11 is provided a vacuum gasexhaust hole, which is connected to vacuum pump 28 via gas exhaust ratecontrolling valve 27.

In the process chamber part of the vacuum chamber 11, there is provideda spectro-photoelectric converter 30, which detects the light emittedfrom the plasma 32 formed between the plate antenna 13 and sample stage24 and converts a light of specified wavelength to electric signals. Theelectric signals emitted from the spectro-photoelectric converter 30 isinput to controller 31. The controller 31 carries out a calculationmentioned later, and outputs the electric signals for controlling theflow rate controlling valves 17, 18 and 19 and the high-frequencyelectric sources 16 and 25. The vacuum chamber 11 is provided withvacuum gauge 29. Although not shown in the figures, the detected signalsare input to the controller 31, and the controller 31 controls the gasexhaust rate controlling valve 27.

The etching process chamber having the construction of FIG. 1 is setaround the vacuum carrying chamber 6 as shown in FIG. 2, as etchingprocess chambers 10 a and 10 b. Around the vacuum carrying chamber 6 areprovided load lock chamber 5 a and unload lock chamber 5 b. The loadlock chamber 5 a and unload lock chamber 5 b are connected toatmospheric air unit 3. The atmospheric air unit 3 is provided withatmospheric air carrying robot 4, and wafer 2 is carried by the aircarrying robot 4 between cassette 1 a or 1 b and load lock chamber 5 aor unload lock chamber 5 b. The vacuum carrying chamber 6 is providedwith a vacuum carrying robot 7, and wafer 2 is carried by the vacuumcarrying robot 7 between the load lock chamber Sa or unload lock chamber5 b and etching process chamber 10 a or 10 b.

In the apparatus having the above-mentioned construction, wafer 2 iscarried from the cassette 1 a, for example, into etching process chamber10 a as shown at FIG. 2. After carrying the wafer 2, the wafer 2 is heldon the sample stage 24, and set to a position of prescribed height bythe stage which can move upward and downward. The wafer 2 is maintainedat a prescribed temperature by a sample temperature control equipment.After reducing the inner pressure of vacuum chamber 11 by the use ofvacuum pump 28, the flow rate controlling valves 17, 18 and 19 arecontrolled to introduce the process gas (etching gas in this case) intothe process chamber from the gas feeding sources 20, 21 and 22 via thegas feeding line 14, and adjusted to a desired pressure. Afteradjustment of pressure in the process chamber, a high-frequency power (ahigh-frequency power of 450 MHz, for example) is oscillated fromhigh-frequency electric source 16. The high-frequency power oscillatedfrom the high-frequency electric source 16 propagates through thecoaxial line 15 and is introduced into the process chamber via plateantenna 13 and dielectric body 12. The electric field of thehigh-frequency electric power introduced into the process chambergenerates a plasma 32 at a low pressure in the process chamber, throughinteraction with the magnetic field formed in the process chamber by themagnetic field-generating coils 23 a and 23 b, such as solenoid coils.When a magnetic field having a strength capable of inducing an electroncyclotron resonance effect (for example, 160 G) is formed in the processchamber, a plasma can be generated especially efficiently.Simultaneously with generation of plasma, a high-frequency power havinga frequency of, for example, 800 KHz, is input to the sample stage 24 bythe high-frequency electric source 25. By this, an incident energy intowafer 2 is given to the ion in plasma 32, the ion enters the wafer 2,and an anisotropic etching of wafer 2 is promoted.

Next, an etching process of insulating film between layers composed ofan organic insulating film used in the dual damascene process using theabove-mentioned apparatus will be explained by referring to FIGS. 3 and4.

First, an unprocessed wafer 2 is carried into the first etching processchamber 10 a (Step 101). At this time, the unprocessed wafer 2 is in astate that, as shown in FIG. 4(a), a patterned photoresist is formed onan unprocessed hard mask 45. The wafer 2 is in a state that a multilayerinterconnect wiring is formed on a substrate, provided that in this casethe underlayer organic insulating film 41 (insulating film betweenlayers), underlayer interconnect wiring 42 and underlayer hard masklayer 43 have already been processed. On the underlayer hard mask 43, anorganic insulating film 44 which is an interlayer insulating film to beprocesses from now (an organic film having a low dielectric constant of2.6-2.7, such as SiLK™ manufactured by Dow Chemicals) and a hard mask 45(in this case, a dual hard mask made of SiN film/SiO₂ film) are formedin the form of films. As an uppermost layer, a patterned photoresist 46is formed.

Next, a process gas for hard mask etching (for example, Ar+O₂+CF gas(C₅F₈)) is fed into the process chamber of the first etching processchamber 10 a, and a plasma etching is carried out. In this etchingprocess, a mask for processing the connection holes for etching theorganic insulating film 44 is formed (Step 102).

In the etching process of hard mask 45, the completion of etching isdetected by the end point detection using emission spectroscopicanalysis (Step 103). FIG. 4(b) illustrates a cross section of processingof the etched material. At this point in time, photoresist 46 mayremain.

Next, wafer 2 which has completed the processing of hard mask 45 iscarried to the second etching chamber 10 b (Step 104).

In the second etching process chamber lob, a process gas for etching oforganic insulating film (ammonia NH₃) is fed into the process chamber toperform a plasma etching. In this etching process, contact holes withunderlayer interconnect wiring 42 are formed on the organic insulatingfilm 44 (Step 105). The photoresist remaining from the preceding step iscomposed of fundamentally identical components with the organicinsulating film, and hence it is also etched off in the etching processof this step.

In the etching process of organic insulating film 44, the completion ofetching is detected by the end point detection using emissionspectroscopic analysis (Step 106). FIG. 4(c) illustrates the crosssection of processing of the etched material. At this time, photoresist46 has been removed, so that the connection hole 47 reaches theunderlayer interconnect wiring 42.

The wafer 2 which has completed the etching processing of organicinsulating film 44 is returned into the original cassette 1 a (Step107).

When all the wafers 2 in the cassette 1 a have been processed andreturned into cassette 1 a as above, a preparation for processing theinterconnect wiring trench on the organic insulating film 44 is started.Cassette 1 a containing the wafers 2 which have completed the processingof contact hole 47 are sent to other apparatus, such as washingapparatus, resist-coating apparatus, light-exposing apparatus,developing apparatus, etc. By these apparatuses, a photoresist in whicha pattern of wiring trench is patterned on hard mask 45 is formed onwafer 2 in the cassette 1 a (Step 108).

Subsequently, cassette 1 a containing the wafer 2 having the patternedphotoresist thereon is set to the atmospheric air unit 3 of the plasmaetching apparatus (Step 111).

After setting the cassette 1 a, wafer 2 is carried into the firstetching process chamber 10 a (Step 112). At this time, the wafer 2 has apatterned photoresist 48 formed on hard mask 45, as shown in FIG. 4(d).

Subsequently, the same process gas for hard mask etching as in Step 102(for example, Ar+O₂+CF gas (C₅F₈)) is fed into the process chamber ofthe first etching process chamber 10 a to carry out a plasma etching. Inthis etching treatment, a mask for processing of wiring trench foretching the organic insulating film 44 is formed (Step 113).

Completion of the etching processing of hard mask 45 is detected by theend point detection by emission spectroscopic analysis (Step 114). FIG.4(e) shows the cross section of processing of the etched body. In hardmask 45, openings for wiring trenches of which opening diameter isgreater than that of contact hole 47 are formed. At this point in time,photoresist 46 may remain.

Subsequently, the wafer 2 which has completed the processing of hardmask 45 is carried into the second etching process chamber 10 b (Step115).

A process gas for the etching treatment of organic insulating film(hydrogen gas (H₂)+nitrogen gas (N₂)) is fed into the process chamber ofthe second etching process chamber 10 b to carry out a plasma etching.By this etching process, a wiring trench having a prescribed depth isformed in the organic insulating film 44 (Step 116). Since this etchingprocess uses no etching stopper layer, flattening of the etching bottomsurface is important and, at the same time, uniformity of etch depthwithin the wafer is important. The conditions of process and the methodfor controlling the process in this etching process will be mentionedlater. The photoresist 48 remaining from the preceding step is etchedoff altogether in the etching process of this step, in the same manneras above.

Completion of the etching processing of organic insulating film 44 isdetected by an end point detecting method such as mentioned in U.S.patent application Ser. No. 09/946,504 (JP Application 2001-28098) whichcomprises using a wavelength pattern of differentiated value ofinterference light, measuring the film thickness from the standardpattern and the actual pattern at the time of actual processing andcalculating the depth of etching (Step 117). FIG. 4(f) illustrates thecross section of processing of the etched body. At this point in time,photoresist 46 has been removed, and wiring trench 49 having aprescribed depth is formed.

The wafer 2 which has completed the etching processing of organicinsulating film 44 is returned into the original cassette 1 a (Step118).

By carrying out the steps mentioned above, a processing of organicinsulating film according to dual damascene process can be put intopractice. With the plasma etching apparatus of the present example, twoetching process chambers can be used, and therefore the etching of hardmask 45 for processing of contact hole and the etching of organicinsulating film 44 can be carried out continuously. Further, the etchingof hard mask 45 for processing of wiring trench and the etching oforganic insulating film 44 can be carried out continuously by merelychanging over the process gas of the second etching process chamber.Thus, a processing of organic insulating film according to dualdamascene process can be performed with only one apparatus.

Further, if three etching process chambers are provided around thevacuum carrying chamber 6 so as to carry out the etching of hard mask 45for contact holes and wiring trenches at the second process chamberplaced at the central position, the etching of the contact holes of theorganic insulating film 44 at the first etching process chamber placedin the neighborhood (for example, on the left side) of the secondetching process chamber, and the etching of the wiring trenches oforganic insulating film 44 at the third etching process chamber placedin the neighborhood (for example, on the right side) of the secondetching process chamber, the processes of the respective etching processchambers can be fixed. Further, it is also possible to use the secondand first etching process chambers alternately to carry out a continuousprocess with the second and first etching process chambers or with thesecond and third etching process chambers. By taking such a measure, itbecomes possible to store the wafers for contact holes in cassette 1 aand the wafers for wiring trenches in cassette 1 b and thereby to carryout the etching of the contact holes and wiring trenches simultaneouslywith only one apparatus (simultaneous processing).

Further, if four etching process chambers are provided around the vacuumcarrying chamber 6, the etching of the hard mask 45 for contact holesand etching of the contact holes of organic insulating film 44 can becarried out continuously at respective process chambers for exclusiveuse, by the use of the first and second etching process chambers; andthe etching of the hard mask 45 for wiring trenches and etching of thewiring trenches of organic insulating film 44 can be carried outcontinuously at respective process chambers for exclusive use, by theuse of the third and fourth etching process chambers. By taking such ameasure, it becomes possible to store the wafers for contact holes incassette 1 a and the wafers for wiring trenches in cassette 1 b andthereby to carry out the etching of the contact holes and wiringtrenches in parallel with only one apparatus.

In the present example, the load rock chamber 5 a is distinguished fromunload rock chamber 5 b. However, it is also possible to use the rockchamber 5 a for carrying in and carrying out the wafers of cassette 1 aand to use the rock chamber 5 b for carrying in and carrying out thewafers of cassette 1 b. By taking such a measured, the carrying route ofwafers can be made shortest in the above-mentioned simultaneous andin-parallel processes in the cases of providing three or four etchingprocess chambers.

Subsequently, the etching method of wiring trenches of organicinsulating film 44 in the above-mentioned Step 116 will be explained byreferring to FIGS. 5 to 10.

In the etching of wiring trench, the etching characteristics wereevaluated for the five cases shown in Table 1.

TABLE 1 Gas flow rate (cc/min) Inner pressure Etch CN/H HydrogenNitrogen Ammonia of process rate intensity Sub-trench Case gas gas gaschamber (Pa) (nm/min) ratio coefficient 1 200 10 0 3 122 0.6 96 2 200 020 3 154 0.7 100 3 50 50 0 3 159 4.5 122 4 50 0 50 3 189 6 126 5 200 100 10 127 3.7 120

In Cases 1 to 4, the process pressure was adjusted to a pressure lowerthan 10 Pa (3 Pa in these cases), and species and flow rate of gas werevaried. In Cases 1 and 3, nitrogen gas was used as the etching gas fororganic insulating film and a mixture of hydrogen gas (H₂) and nitrogengas (N₂) was used. In Cases 2 and 4, ammonia gas was used as an etchinggas for organic insulating film, and a mixture of hydrogen gas (H₂) andammonia gas (NH₃) was used. In Case 1, the quantity of hydrogen gas was20 times that of nitrogen gas functioning as etchant for organicinsulating film. In Case 2, the quantity of hydrogen gas was 10 timesthat of ammonia gas functioning as etchant for organic insulating film.In Case 3, the quantity of hydrogen gas was the same as that of nitrogengas functioning as etchant for organic insulating film. In Case 4, thequantity of hydrogen gas was the same as that of ammonia gas functioningas etchant for organic insulating film. In Case 5, the same process gasas in Case 1 was used, and the process pressure was 10 Pa or more (10 Pain this case). Throughout all the cases, the power of high-frequencypower for plasma generation was 1 kW.

These experimental results demonstrate the following facts:

(1) Etch rate can be improved by using ammonia gas as etching gas, ascompared with the other case.

(2) Sub-trenching coefficient can be improved by increasing theproportion of hydrogen gas as compared with that of etchant gas. Theterm “sub-trenching coefficient” means the following ratio expressed interm of percentage:

(Etch Rate in Areas Near the Etched Sidewall/Etch Rate at Center ofTrench)

When the percentage defined above is 100% or less, it is known that nosub-trenching has occurred.

(3) For preventing the sub-trenching, it is necessary that the mixingratio of the H-component gas to the N-component gas (H-gas/N-gas) in thetreating gas is 10 or more, the total flow rate is 200 cc/minute ormore, and the emission spectral intensity ratio (CN/H) is 1 or less.These conditions further mean that, in order to prevent thesub-trenching, the pressure in the etching process chamber has to belower than 10 Pa.

By measuring the emission spectral intensity of the plasma in the casesinducing no sub-trenching and the cases inducing sub-trenching, it hasbeen found that characteristic peaks of light emission intensity appearat wavelengths of 388 nm and 486 nm. These two spectra are assignable tocyan molecule (CN) having a wavelength of 388 nm and hydrogen atom (H)having a wavelength of 486 nm.

As a result, it can be concluded that the etching conditions inducing nosub-trenching are those of Case 1 and Case 2. FIG. 5 illustrates resultof measurement of light emission intensities of cyan molecule (CN) whichis reaction product in the plasma formed under the subtrenching-freeconditions and hydrogen atom (H), wherein it is known that hydrogen atom(H) is higher than cyan molecule (CN) in light emission intensity. Theetching conditions in this case are as follows; H₂: 300 sccm, N₂: 10sccm, pressure of treatment: 3 Pa, high-frequency power for formation ofplasma: 1 kW.

The fact that hydrogen atom (H) is higher than cyan molecule (CN) inlight emission intensity means that, in the plasma, the quantity ofhydrogen atom (H) (in other words, H radical) is larger than thequantity of cyan molecule (CN). Thus, it is considered that the state ofreaction is as shown in FIG. 7. That is, in the plasma, the quantity ofH radical is larger than that of N ion as an etchant. Upon incidence ofN ion into the etched surface, the N ion reacts with organic insulatingfilm 44 to form cyan molecule CN as a reaction product. The cyanmolecule CN which has once left the wafer 2 again enters the wafer 2 andis deposited on the bottom surface of etched part. When H radicaloriginated from the plasma is contacted with the deposited CN molecule,there occurs a reaction to form a more volatile reaction product HCNwhich vaporizes from the etched surface and is exhausted. Thus, theprocess of etching progresses regardless of the influence of depositiondistribution of reaction product (in this case, cyan molecule CN) in theetched part (deposition distribution: the reaction product is morereadily deposited on the central part of trench than in the neighborhoodof sidewall), and thereby the sub-trenching can be prevented.

Contrariwise, sub-trenching occurs in the other cases (Case 3, 4 and 5).If the light emission intensities of cyan molecule (CN) and hydrogenatom (H) in the plasma are measured and compared with those under theconditions inducing sub-trenching, it is found that intensity ofhydrogen atom (H) is lower than that of cyan molecule (CN) as shown inFIG. 6. The etching conditions in these cases are as follows; H₂: 35sccm, N₂: 35 sccm, treating pressure: 3 Pa, high-frequency power forgeneration of plasma: 1 kW. It is considered that the state of reactionis as shown in FIG. 8 under such conditions. That is, the plasmacontains a large quantity of N ion, and a high etch rate can beachieved. At the same time, the quantity of CN is also large, andre-deposition of CN onto the etched surface takes place. Since thereaction product is more readily deposited onto the central part ofbottom surface than in the bottom surface near the sidewall of etchedsurface, the bottom surface near the sidewall is more readily etched toinducing sub-trenching. Further, it is also considered that N ion havinga higher incidence energy into wafer is concentrated into theneighborhood of sidewall of the etched part, and thereby sub-trenchingoccurs.

FIG. 9 illustrates the relation between light emission intensity ratiobetween cyan molecule (CN) and hydrogen atom (H), namely CN/H, and thesub-trenching coefficient. It is understandable from FIG. 9 that theCN/H ratio at which the sub-trenching coefficient becomes 100% or lesswhere no sub-trenching occurs is 1 or less, roughly saying. Additionallysaying, the point in the case shown in Table 1 is the point to whichcase number is attached. The state of light emission intensity shown inFIG. 5 is point (a), and the state of light emission intensity shown inFIG. 6 is pint (b).

Next, the controlling method for preventing the sub-trenching by the useof the controlling apparatus 31 shown in FIG. 1 is explained byreferring to FIG. 10.

In the above-mentioned Step 116 of the etching for forming wiring trenchin an organic insulating film, the emission spectra from the cyanmolecule CN and hydrogen atom H from the plasma are converted toelectric signals by means of a photoelectric converter, and therespective intensities are measured (Step 121). From the measuredintensities of CN and H, intensity ratio CN/H is calculated (Step 122).Subsequently, whether or not the intensity ratio CN/H is smaller than 1or less is judged (Step 123). If the judged intensity ratio is 1 orless, the etching is continued without changing the conditions (Step129). After continuing the etching, whether the desired quantity ofetching has been reached or not is judged according to theabove-mentioned method of end point detection using film thicknessmeasurement (Step 130). When the desired quantity of etching is not yetreached, the procedure is turned back to Step 121 and the processing iscontinued. When the quantity of etching has reached the desired valueand the end point of etching has been detected, the etching process iscompleted.

On the other hand, when emission intensity ratio is greater than 1 inStep 123, the flow rate controlling valves are operated to increase theflow rate of hydrogen gas (Step 124). Although it is also allowable todecrease the flow rate of nitrogen gas, such an operation causes adecrease in etch rate. Therefore, it is more desirable to change theflow rate of hydrogen gas. Although not shown in the figure, thecontroller 31 controls the gas exhaust rate controlling valve 27 so asto give a constant process pressure. Subsequently, whether or not thevalue of flow rate control has reached the upper limit, or maximum, isjudged (Step 125). So far as the value of flow rate control has notreached the maximum value, the procedure is turned back to Step 121, andcheck of intensity ratio is repeated.

In the case where the value of flow rate control is maximum and it isimpossible to increase the quantity of hydrogen gas further, theelectric power for plasma generation is increased (Step 126). By takingsuch a measure, the decomposition of hydrogen molecule in the plasma isenhanced, a larger quantity of H radical is formed, and light emissionintensity of H radical is enhanced. Subsequently, whether the output ofthe high-frequency power from the high-frequency electric source forplasma generation is maximum or not is judged (Step 127). So far as theoutput of high-frequency power has not yet reached the maximum, theprocedure is turned back to Step 121 and the check of intensity ratio isrepeated.

On the other hand, in the case where the output of high-frequency poweris maximum and the power value cannot be enhanced further, output of thehigh-frequency power of bias-application to wafer is lowered (Step 128).

As above, the control is carried out by increasing hydrogen gas in thefirst stage and increasing the power for plasma generation in the secondstage. Accordingly, occurrence of sub-trenching is suppressed withoutlowering the etch rate-caused parameter. Thus, sub-trenching can beprevented while maintaining the prescribed etch rate.

As has been mentioned above, according to the present example, a processpressure lower than 10 Pa is adopted, and the reaction product CN whichis apt to be re-deposited at the time of etching is positively convertedto highly volatile HCN through reaction with the hydrogen component andthen exhausted. Accordingly, the method of the present example has aneffect that etching of organic insulating film can be performed whilepreventing micro-trenching.

Further, according to the present example, in the etching of organicinsulating film having a low dielectric constant, trench or hole can beflattened without forming sub-trench, and therefore a trench forelectric wiring can be formed on semiconductor LSI chips without usingan etch stop layer.

Further, according to the present example, etching process of organicinsulating film can be carried out without sub-trenching by using amixture of nitrogen gas and hydrogen gas as a treating gas under atreating pressure lower than 10 Pa and controlling the light emissionintensity ratio between emission spectra of cyan molecule CN andhydrogen atom H in the plasma so as to come to 1 or less.

Further, by increasing and controlling the flow rate of hydrogen gas sothat the light emission intensity ratio CN/H comes to 1 or less, thesub-trenching can be suppressed without decreasing the etch rate oforganic insulating film.

Further, by increasing and controlling the output of the high-frequencypower for plasma generation so that the light emission intensity ratioCN/H comes to 1 or less, the quantity of H radical in plasma can beincreased and thereby sub-trenching can be suppressed without loweringthe etch rate of organic insulating film.

Further, since a gaseous mixture of nitrogen gas and hydrogen gas isused as the process gas, the gas formulation is simple, and the lightemission intensity ratio CN/H can easily be controlled by controllingthe flow rate of process gas.

In the present example, a mixture of nitrogen gas and hydrogen gas wasused as the process gas for trench-processing of organic insulatingfilm. However, the same effect as above can be obtained also by using agaseous mixture of ammonia gas and hydrogen gas and making the lightemission intensity ratio CN/H in the plasma come to 1 or less.

In the present example, an UHF magnetic field type plasma etchingapparatus using an electric source of frequency 450 MHz was used as thehigh-frequency electric source for plasma generation. However, the sameeffect as above can also be achieved with an apparatus of otherdischarge methods such as micro wave ECR, capacitive coupled, inductivecoupled, magnetron, etc., so far as the apparatus is capable of etchingan organic insulating film at a process pressure lower than 10 Pa, bybalancing between cyan molecule and hydrogen atom.

As above, according to this invention, there can be achieved an effectthat an organic insulating film can be etched while suppressing thedeposition of reaction product onto inside of process chamber andpreventing the microtrenching.

It should be further understood by those skilled in the art that theforegoing description has been made on embodiments of the invention andthat various changes and modifications may be made in the inventionwithout departing from the spirit of the invention and the scope of theappended claims.

What is claimed is:
 1. An etching method for forming a trench having aprescribed depth in an organic insulating film, comprising the step of:providing a wafer having an organic insulating film thereon, the wafernot having an etching stopper layer around the prescribed depth of theorganic insulating film; generating a plasma from a gas containinghydrogen and nitrogen; measuring a light emission spectral intensityratio between cyan molecules and hydrogen atoms in the plasma; etching aportion of the organic insulating film with the plasma to the prescribeddepth less than a thickness of the organic insulating film with theplasma; and controlling the plasma to keep a measured value of the lightemission spectral intensity ratio at a value not exceeding a prescribedvalue so as to form the trench in the organic insulating film to theprescribed depth while suppressing microtrenching.
 2. The etching methodaccording to claim 1, wherein the wafer is a semiconductor wafer.
 3. Theetching method according to claim 1,wherein the semiconductor wafercomprises underlayer interconnect wiring under the organic insulatingfilm.
 4. The etching method according to claim 1, wherein the gascontaining hydrogen and nitrogen is a molecular gas.
 5. The etchingmethod according to claim 4, wherein the molecular gas contains nitrogengas and hydrogen gas.
 6. The etching method according to claim 4,wherein the molecular gas contains ammonia gas and hydrogen gas.
 7. Theetching method according to claim 1, wherein the step of controlling theplasma comprises controlling the plasma to keep the emission spectralintensity ratio CN/H at 1 or less, wherein H represents a light emissionspectral intensity of hydrogen atom at a wavelength of about 486 nm andCN represents a light emission spectral intensity of cyan molecule at awavelength of about 388 nm in the plasma.
 8. The etching methodaccording to claim 7, wherein the plasma is controlled by controlling aflow rate of hydrogen containing gas.
 9. The etching method according toclaim 7, wherein the plasma is controlled by controlling a flow rate ofhydrogen containing gas and controlling electric power for generatingthe plasma.
 10. The etching method according to claim 9, furthercomprising adjusting a pressure in an etching process chamber in whichthe organic insulating film is etched to a pressure lower than 10 Pa.11. The etching method according to claim 5, wherein a mixing ratio ofthe hydrogen gas to the nitrogen gas is 10 or more.
 12. The etchingmethod according to claim 11, wherein a total flow rate of the hydrogengas and the nitrogen gas is 200 cc/minute or more.
 13. The etchingmethod according to claim 6, wherein a mixing ratio of the hydrogen gasto the ammonia gas is 10 or more.
 14. The etching method according toclaim 11, wherein a total flow rate of the nitrogen gas and the ammoniagas is 200 cc/minute or more.